Construction and Building Materials 25 (2011) 3746–3752

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Construction and Building Materials

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Induction healing of asphalt mastic and porous asphalt concrete

Quantao Liu a,⇑, Álvaro García a, Erik Schlangen a, Martin van de Ven b

a Delft University of Technology, Faculty of Civil Engineering and Geosciences, Micromechanics Laboratory (MICROLAB), Stevinweg 1, 2628 CN Delft, The Netherlandsb Delft University of Technology, Faculty of Civil Engineering and Geosciences, Road and Railway Engineering, Stevinweg 1, 2628 CN Delft, The Netherlands

a r t i c l e i n f o

Article history:Received 1 December 2010Received in revised form 14 March 2011Accepted 11 April 2011Available online 4 May 2011

Keywords:MasticPorous asphalt concreteInduction heatingHealingSteel wool

0950-0618/$ - see front matter � 2011 Elsevier Ltd. Adoi:10.1016/j.conbuildmat.2011.04.016

⇑ Corresponding author. Tel.: +31 (0) 15 2788078.E-mail addresses: quantao.liu@tudelft.nl, liuquanta

a b s t r a c t

The objective of this paper is to detect the healing effect of asphalt mastic and porous asphalt concretecaused by induction heating. It was found that the broken mastic beams could be healed many timesby induction heating. Moreover, the stiffness of porous asphalt concrete recovered more and faster wheninduction heating was applied to the samples. It was also found that fatigue life of porous asphalt con-crete was significantly extended by induction heating. Based on these findings, it was concluded thatthe self healing rate of asphalt mastic and porous asphalt concrete can be increased by induction heating.

� 2011 Elsevier Ltd. All rights reserved.

1. Introduction

Porous asphalt was first used in the Netherlands in 1972 [1] andit was decided to start applying porous asphalt wearing courses ona large scale in 1987 [2]. Up to now, more than 90% of the top lay-ers of highways in the Netherlands were laid with porous asphaltconcrete and the goal is 100% [3]. Porous asphalt 0/16 is mostlyused in a thickness of 50 mm and a minimum air voids contentof 20%. This open nature of porous asphalt concrete brings signifi-cant benefits. The first important advantage of porous asphalt con-crete is to reduce the traffic noise in 2–3 dB compared to typicaldense graded asphalt concrete roads [2,4,5]. Another importantadvantage of porous asphalt concrete is drainage of water [6]. Dur-ing rainfall events, water drains through porous asphalt concreteinto the stone bed and slowly infiltrates into the soil, which canimprove the visibility and driving safety [7]. However, the attrac-tive features of porous asphalt concrete do not last long becauseof clogging, stripping, and accelerated aging [8]. Raveling of porousasphalt concrete, which is the loss of aggregate particles from theroad surface, is the main problem on surface wearing courses [9].It is caused by an increase of stiffness, reduction of relaxationcapacity and formation of micro-cracks in the binder due to aging[10]. Traffic will finally remove the particles from the surface.Raveling decreases the road performance and requires early main-tenance. Due to raveling, the service life of porous asphalt road ismuch shorter (10–12 years) than that of dense graded asphaltroads (18 years) [3,11]. This phenomenon is the cause for mainte-

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o82@126.com (Q. Liu).

nance or renewing of the top layer in about 76% of the cases [12]. Ifthe problem of raveling can be prevented or delayed, the servicelife of porous asphalt wearing course will be greatly extended.

It is well known that asphalt concrete is a self healing material[13,14]. When subjected to rest periods, asphalt has a potential toheal damage and restore its mechanical properties by closing thecracks inside [15]. There are a number of studies about self-healingasphalt concrete since 1960s [16–19]: Bazin and Saunier foundthat asphalt concrete beams, tested until failure under uniaxialtensile loads could recover 90% of their original resistance whenthey were let to rest under pressure at a temperature of 25 �C[16]. Healing of asphalt concrete can be also found in the field, be-cause cracks observed in winter time can disappear in summertime. Besides, a shift factor required to translate the laboratory fa-tigue life to the in situ fatigue life is also dominated by healing [20].

Healing mechanisms of asphalt concrete have been reported bymany researchers. Phillips proposed a three-step diffusion modelto explain the healing of bitumen: (1) closing of cracks due to wet-ting (adhesion of two crack surfaces together driven by surface en-ergy), (2) closing of cracks due to consolidating stresses andbitumen flow, and (3) the complete recovery of mechanical proper-ties due to diffusion of asphaltene structures [21]. Castro explainedthe healing of asphalt mixes during rest periods by the sol–gel the-ory [22]. At high temperature, healing happens due to the transi-tion from sol to gel of bitumen and, if the rest period is enough,damage recovery will be complete. At low temperature, rest peri-ods do not allow the healing of structural damage created by theloading cycles and recovery would only be partial.

Finally, it is well known that healing of asphalt concrete is atemperature dependant phenomenon. The temperature

Q. Liu et al. / Construction and Building Materials 25 (2011) 3746–3752 3747

dependence of healing mechanisms has been reported by manyresearchers: an increase in the test temperature increases the heal-ing rate and shifts the recovery response to a shorter time [23–25].Based on these mechanisms, conductive porous asphalt concreteused for induction heating has been developed, so that porous as-phalt concrete can regularly repair itself by induction heating andraveling can be avoided or delayed [26–30]. The idea is to add steelfibers (steel wool) to porous asphalt concrete. When small cracksoccur in the material, the temperature can be increased by induc-tion heating via an external source to make the bitumen soft en-ough to start the self healing process. It has been already proventhat asphalt mastic and porous asphalt concrete containing steelwool can be heated quickly with induction heating [26–28]. Forthis reason, the objective of this paper is to detect the healing effectof asphalt mastic and porous asphalt concrete caused by inductionheating.

2. Materials

In this research, asphalt mastic beams and gyratory compacted porous asphaltconcrete specimens have been used. The beams have the size shown in Fig. 1 and atriangular notch in the center to create a weak point and force the samples to breakalways under the same conditions. To make the mastic beams, the followingmaterials are used: five fractions (<0.120, 0.120–0.250, 0.250–0.5, 0.500–1.0, 1.0–2.0 mm, 20% by weight of each size) of crushed sand, with density 2.67 g/cm3,70/100 pen bitumen, obtained from Kuwait Petroleum, (density 1.032 g/cm3) andsteel wool type 000, chopped by hand, always by the same operator, with diametersbetween 6.38 lm and 8.89 lm and medium length 7 mm. This steel wool had anapproximate density of 7.6 g/cm3 and an electrical resistivity of 7 � 10�7 X cm. Inaddition, the sand–bitumen volumetric ratio was 1.6:1 and the content of steelwool type 000 was 5.66% by volume of bitumen.

The gyratory compacted porous asphalt concrete specimens have a diameter of100 mm and a height of 50 mm. The materials used to make them were quarrymaterial (Bestone, Bremanger Quarry, Norway) (size between 2.0 mm and22.4 mm and density 2.77 g/cm3), crushed sand (size between 0.063 mm and2 mm and density 2.69 g/cm3), and filler type Wigro 60 K (size <0.063 mm anddensity 2.64 g/cm3). The bitumen used was 70/100 pen, obtained from KuwaitPetroleum (density 1.032 g/cm3). Two kinds of steel wool were used in the mix-ture. At the beginning of this study, steel wool type 000, as used in the mastic test,was introduced into the asphalt mixture. This steel wool content in the sampleswas 10% by volume of bitumen. After optimizing the steel wool, type 00 was foundbetter than type 000 to improve the strength and particle loss resistance of porousasphalt concrete [31]. So, in the following tests steel wool type 00 was usedinstead of type 000. The amount of steel wool type 00 that used in this studywas 8%, by volume of bitumen in the mixture. Steel wool type 00 has diametersbetween 8.89 lm and 12.7 lm, an approximate density of 7.6 g/cm3 and an elec-trical resistivity of 7 � 10�7 X cm. Additionally, it was chopped to have a length of9.5 mm.

Moreover, porous asphalt PA 0/16, the most commonly used mixture in theNetherlands, was chosen for this research. Its composition was fixed based on theDutch Standard, RAW 2005 (Table 1) and was mixed at 160 �C. To find the optimummixing time, the material was mixed for 10 min, 12 min, 15 min and 20 min in aHobart Mixer, and compacted to have an air void content of 21% with a Gyratorcompactor, which can control the height of the specimen to obtain the target voidcontent according to the maximum theoretical density, the calculated density of thespecimen after compaction and the weight of the mixture. To check the fibers dis-tribution, CT-Scan images of the samples were taken (Fig. 2). Bright dots in Fig. 2aand b are clusters of steel wool, which means a bad distribution of steel wool in theconcrete. The clusters disappear in Fig. 2c and d where the material is much morehomogeneous. For this reason, all the samples were mixed for 15 min. In the lateststudy, it was found that the mixing procedure could be optimized a lot. By first

15 mm

125 mm

25 mm

Fig. 1. Asphalt mastic beam

mixing the bitumen with steel wool and then adding the aggregates and filler,the mixing time can be reduced to 3 min. However, this mixing procedure is notyet used in this study.

3. Experimental methods

In this research, the basic approach to heal asphalt mastic andporous asphalt concrete consists of damaging the samples, andthen, heat them via induction energy. This cycle can be repeatedmany times. Healing is the difference between the mechanicalresistance before and after heating. Strength recovery, stiffnessrecovery and fatigue life extension were used to quantify the heal-ing rate of asphalt mastic and porous asphalt concrete.

3.1. Temperature measurements

The temperature changes were measured with a 320 � 240 pix-els, full color infrared camera. The induction heating experimentswere performed by using an induction heating system with acapacity of 50 kW and at a frequency of 70 kHz. The system wasnot fully optimized, which had however no influence on the re-search objectives: show how conductive asphalt can be healedthrough induction energy.

To get a better understanding of the induction heating system,in Fig. 3 induction heating images of a porous asphalt concretesample are shown. The distance between the coil of the inductionheating machine and the top surface of the sample was 32 mm. Thehighest temperature on the top surface of the samples was approx-imately 120 �C after 2 min heating. The temperature of the porousasphalt concrete sample decreased vertically from top to bottom.With this temperature distribution, the road surface can be healedwithout affecting the structure of the lower part. The temperatureis almost homogeneous in the horizontal direction.

3.2. Mastic tests

Healing in asphalt mastic was characterized by testing thestrength recovery of beam samples after fracture. The test proce-dure is shown in Fig. 4. First, 5 mastic beams were frozen at�20 �C and broken into two pieces by means of three points bend-ing tests. This temperature was chosen to create a brittle fracturein the samples. Then, both pieces were put together in the samemold where they were originally made and induction-heated dur-ing 2 min, until the temperature was close to 120 �C in the surfaceof the samples. Finally, the samples were frozen to �20 �C and bro-ken again using three points bending tests. This process was re-peated until the beams did not resist any more loads. In theseexperiments, the distance between the coil of the induction heat-ing machine and the top surface of the sample was 32 mm.

3.3. Indirect tensile tests of porous asphalt concrete

Before testing the healing in porous asphalt concrete, indirecttensile tests were done to study the mechanical property

used in the research.

Table 1Composition of PA 0/16 mixture based on the Dutch standard (RAW 2005).

Sieve size (mm) 16.0 11.2 8.0 5.6 2.0 0.063 <0.063

% Ret. by weight 4 21 32 23 5 10.5 4.5Bitumen 70/100, 4.5% by wt. of aggregate

a b

c d

1 cm

1 cm

1 cm

1 cm

Fig. 2. CT-Scan images of porous asphalt concrete samples with different mixing times: (a) 10 min; (b) 12 min; (c) 15 min; (d) 20 min.

Vertical temperature distribution

Horizontal temperature distribution

Fig. 3. Infrared images of a porous asphalt concrete sample.

3748 Q. Liu et al. / Construction and Building Materials 25 (2011) 3746–3752

Fig. 4. Test procedures for strength recovery of mastic beam.

1000

4000

7000

10000

13000

0 2000 4000 6000 8000 10000

Loading cycles

Res

ilient

mod

ulus

Mpa

C1 C2

Fig. 5. Fatigue recovery of porous asphalt concret.

0

2

4

6

8

10

12

14

16

0,E+00 1,E+04 2,E+04 3,E+04 4,E+04 5,E+04 6,E+04 7,E+04 8,E+04

Loading time (s)

Verti

cal d

efor

mat

ion

(mm

)

3 hours loading 8 hours loading

Fig. 6. Damage loading time in stiffness recovery testing.

Q. Liu et al. / Construction and Building Materials 25 (2011) 3746–3752 3749

difference between plain porous asphalt concrete samples andsamples containing steel wool. First, indirect tensile strength ofsamples was measured at 5 �C by applying a load at a rate of50 mm per minute. The test procedures are described in AmericanAssociation of State Highway and Transportation Officials (AASH-TO) provisional standard TP 9-95. After the tests, indirect tensilestrength of the samples could be calculated using the followingequation:

ITS ¼ 2FpDH

ð1Þ

where ITS is the indirect tensile strength in Pascal, F is the total ap-plied vertical load at failure in Newton, D is the diameter of speci-men in meter and H is the height of specimen in meter.

Furthermore, indirect tensile fatigue resistance of both plainsamples and samples containing steel wool were studied. These fa-tigue tests were done with four loading levels at 5 �C with a fre-quency of 8 Hz.

3.4. Healing tests of porous asphalt concrete

To prove that porous asphalt concrete can be healed via induc-tion heating, indirect tensile fatigue tests at 5 �C, with rest periodsto heat them with induction energy, were done. The idea was tointroduce some damage to the material, then the samples wereinduction-heated and they were let to rest some time. In this re-search, fatigue tests applied a 0.2 s haversine load followed by arest period of 0.3 s at a frequency of 8 Hz. Finally, a Poisson’s ratioof 0.22 was assumed for this porous asphalt concrete to determineits resilient modulus (stiffness).

To have a first impression about the healing capacities of porousasphalt concrete, indirect tensile fatigue tests were conducted inthe samples containing 10% steel wool type 000. For these tests,the maximum load applied was 0.82 MPa. Fatigue tests werestopped when the resilient modulus of the sample reduced to70% and 80% of its original value. Then, the samples were induc-tion-heated for 2 min and they were let to rest for 24 h. Finally, fa-tigue tests were continued until the resilient modulus reduced to70% and 80% of its initial value for a second time. After the tests,two numbers of loading cycles C1 and C2, were obtained (Fig. 5).Healing index (HI) is defined as C2 divided by C1, where 100%means the entire healing of damage and 0% means no healing at all.

Second, to quantify the healing recovery with different restingtimes, the original stiffness of the samples containing 8% steel wooltype 00 was measured at 5 �C. Then, a cyclic load of 0.60 MPa, at afrequency of 8 Hz, was applied to the samples during 3 or 8 h,

respectively. After this, the specimens were let to rest during dif-ferent time, from 0 to 20 h. Finally, the stiffness of each samplewas monitored, and the comparison with the original stiffnesswas used as the healing indication. In addition, a third set of sam-ples was induction-heated immediately after the 8 h cycle loadingand before the resting period. These samples were heated during1.5 min, until their medium surface temperature was 70 �C. This

3,2

3750 Q. Liu et al. / Construction and Building Materials 25 (2011) 3746–3752

heating process was repeated on both faces of the samples. To havea look at the damage extent after loading 3 or 8 h, the fatigue curvewas shown in Fig. 6, where 3 or 8 h corresponds to 0.14 or 0.37times of the fatigue life, respectively.

Finally, fatigue of porous asphalt concrete containing 8% steelwool type 00 was also used to characterize the healing effect andto compare the natural healing, with the induction healing and sam-ples with no healing at all. These fatigue tests were done at 5 �C, and0.60 MPa of maximum load. For comparison purposes, three sets oftests were prepared. In the first one, fatigue experiments were rununtil failure. In the second one, 8 h of cyclic loading were appliedto the specimens; then they were let to rest during 20 h and finally,fatigue tests were run until failure. The third set of experiments wasthe same as the second one, with the difference that before the rest-ing period, the samples were induction-heated during 1.5 min, untiltheir medium surface temperature was 70 �C. This process was re-peated in both faces of the samples.

2

2,2

2,4

2,6

2,8

3

0 2 4 6 8 10 12 14 16

Fiber volume content (%)

ITS

(Mpa

)

Fig. 8. Indirect tensile strength of porous asphalt concrete.

4. Results and discussion

4.1. Healing of asphalt mastic

The evolution of the mechanical resistance of asphalt masticsamples trough successive damage-healing cycles is shown inFig. 7. This process was repeated until the accumulated damagein the material was too high to continue the healing process. Thestrength recovery of the samples after the first healing is about85% of the original value. In successive cycles, it became stable atabout 70% of the original value. Finally, it decreased sharply afterthe sixth healing. During the induction heating process, it couldbe seen that cracks disappeared because of the flow of bitumen.It could be also observed that the volume of the mixture increasedthrough the cycles, maybe because the heating was excessive andthe air pores in the mixture suffered an expansion. It is not clear ifthe strength levels decreased because the crack represented aweak point or because the sample was suffering some kind ofstructural damage due to the induction heating. This will be a pointfor future research. But, based on these results, it can be concludedthat asphalt mastic containing steel wool can be healed very fastwith induction energy.

4.2. Mechanical properties of porous asphalt concrete

Fig. 8 presents the indirect tensile strength of plain samples andsamples containing steel wool. It is clear that the indirect tensile

0

0,02

0,04

0,06

0,08

0,1

0,12

0,14

0,16

100 %

70 %

0

0,02

0,04

0,06

0,08

0,1

0,12

0,14

0,16

Forc

e (K

N)

100 %

70 %

Number of breaking-healing cycles1 2 3 4 5 6 7

Ultimate resistance evolution

Fig. 7. Stress–strain curves for samples with 5.66% steel wool type 000 (related tothe volume of bitumen) and sand-bitumen ratio 1.60.

strength of porous asphalt concrete can be increased by addingsteel wool, which can be attributed to the reinforcement of steelwool. However, too much steel wool can decrease the strength, be-cause this will result in a bad adhesion between the binder and theaggregates. As it is shown in Fig. 8, the optimum content of fibersto have the highest indirect tensile strength, by volume of bitumenis 8%. In the fatigue test, the fatigue resistance of plain samples andsamples containing 8% steel wool type 00 were compared. Addi-tionally, in Fig. 9, it can be seen that samples containing steel woolhave better fatigue resistance than plain samples: fatigue damagedevelops slowly in samples containing steel wool and they can re-sist higher load. The reason for this is that steel wool increases themechanical properties of the porous asphalt concrete, avoiding theopening of micro-cracks on it.

Fig. 9. Fatigue lines of both types of mixtured studied, with and without steel wooltype 00.

Table 2Healing indexes of the samples studied.

Samples Plain samples (%) Samples with steel wool

Without heating (%) With heating (%)

HI70% 11.42 17.99 23.05HI80% 52.08 83.80 100

0

4

8

12

16

0,E+00 3,E+05 6,E+05 9,E+05Number of loading cycles

Verti

cal d

efor

mat

ion

(mm

)

original

8 hours loading damage

20 hours healing without heating

20 hours healing with 1.5 min heating

H3 H1

H2

Fig. 11. Fatigue life extensions of porous asphalt concrete samples containing 8%steel wool type 00.

Q. Liu et al. / Construction and Building Materials 25 (2011) 3746–3752 3751

4.3. Fatigue recovery of porous asphalt concrete

The healing indexes of plain samples (without fibers) andsamples containing 10% steel wool 000 after 24 h rest are shownin Table 2. Each one of these values has been obtained from threesamples. In this table, HI70% and HI80% mean that fatigue tests werestopped for healing when the resilient modulus of the sample de-creased to 70% and 80% of its original value, respectively. In bothcases, samples with fibers have better healing effect than plainsamples. Additionally, the healing effect of conductive samplesincreases after the induction heating is applied. In the case wherefatigue tests were stopped for healing when the resilient modulusdecreased to 70% of its original value, after 24 h rest, only 11.42%and 17.99% of the damage in plain samples and in samples contain-ing steel wool was healed. But when a 2 min induction heating wasapplied, 23.05% of the damage could be healed in the samples withfibers. In this case, the healing was relatively low because struc-tural damage, such as permanent deformation or broken aggre-gates, has appeared. Induction healing can repair micro-damage,not structural damage, so in this case, it was too late to heal thedamage in the asphalt concrete. But when fatigue tests werestopped when the resilient modulus had reduced to 80% of its ori-ginal value (to avoid structural damage in the sample), 52.08% and83.80% of the damage in plain samples and in samples containingfibers, respectively, were healed after 24 h rest. Finally, with2 min induction heating, the damage in samples containing steelwool could be completely healed.

Results quantifying the healing recovery with different restingtimes are shown in Fig. 10. The medium original stiffness of thesamples containing 8% steel wool type 00 was 14,654 MPa. In thecase where the cyclic load was applied during 3 h, the stiffness de-creased to 11,809 MPa. The stiffness of the sample could recover toits original value after a resting time of 4 h. This happened becausethe damage induced was low enough to allow natural healing. Inthe case where the cyclic load was applied during 8 h, the stiffnessdecreased to 8702 MPa. In this Figure, it can be seen that the max-imum possible stiffness, even after 20 h healing was of 11,544 MPa(78.8% of the original value). This happened because the induceddamage was too high to be naturally repaired. Finally, in the casewhere the cyclic load was applied during 8 h and induction heatingwas used, after 4 h resting (which was needed to cool down thesamples from 70 �C to 5 �C), the stiffness was almost fully recov-ered, with a value of 14,524 MPa (99.1% of the original one). Thestiffness did not change any more over time, which means that full

Fig. 10. Stiffness recoveries of porous asphalt concrete samples containing 8% steelwool type 00.

healing, due to induction heating, had been achieved. It can be con-cluded that induction heating increases the healing capacity ofvery damaged porous asphalt concrete samples containing steelwool and that the resting time needed for full healing is reduced.

Finally, the comparison between natural healing with inductionheating and samples with no healing at all is shown in Fig. 11,where it can be seen that the total fatigue life of porous asphaltconcrete, without rest periods was 617,528 cycles. In the casewhere the samples were let to rest after 8 h fatigue loading, the fa-tigue life after the rest period was 486,864 cycles, which representsa final decrease of 21.16% in the total fatigue life of the material.This means that, although some recovery has happened in the sam-ple (no recovery would mean that the final decrease would be37.31%, the equivalent time to 8 h testing), it has not been com-plete. The overall fatigue life was 717,264 cycles, which was99,736 cycles longer than the original fatigue life without rest per-iod. This extension H1, as shown in Fig. 11 was caused by the restperiod. However, 20 h is a very unrealistic time to let the pavementheal in a real life situation. Finally, in the case when inductionheating was applied after 8 h fatigue loading, the total medium fa-tigue life of the specimens after the rest period was of 622,296 cy-cles, which almost coincides with the total life when compared tothe fatigue experiments without rest periods. In this case, the spec-imens were completely recovered. The whole fatigue time in thiscase was 852,672 cycles, which was 235,144 cycles longer thanthe original fatigue time. This fatigue life extension H2 was causedboth by induction heating and by rest periods. The difference be-tween H2 and H1 was 135,408 cycles, which was the fatigue lifeextension H3 (Fig. 11) caused by induction heating. So, it can beconcluded that the fatigue life was extended by induction healing.

5. Conclusions

The strength (fracture resistance) recovery of asphalt masticwas used to characterize its self healing effect. It was found thatcompletely fractured asphalt mastic beams containing steel wooltype 000 can be healed many times due to induction heating. Dur-ing the induction heating, cracks in asphalt mastic beams disap-peared because of the flow of bitumen.

In addition, the stiffness recovery and fatigue life extensionwere used to quantify the healing rate of porous asphalt concrete.It was found that asphalt concrete samples containing steel woolhad better healing effect than plain samples. In this case, the

3752 Q. Liu et al. / Construction and Building Materials 25 (2011) 3746–3752

stiffness of porous asphalt concrete containing steel wool recov-ered much faster when induction heating was applied. Besides,the resting time needed for full healing was shortened due toinduction heating. In addition, fatigue damage could be totallyhealed via induction heating. The fatigue life of porous asphalt con-crete samples containing steel wool was significantly extended byinduction heating. Based on the strength recovery of mastic, stiff-ness recovery and fatigue life extension of porous asphalt concrete,it was concluded that the self-healing capacity of porous asphaltconcrete was increased and fatigue damage was healed by induc-tion heating.

Heating should not be too early or too late. If it is too early, por-ous asphalt concrete can heal the damage by itself. But, if porousasphalt concrete is heated too late, the healing efficiency will bevery poor, because structural damage such as permanent deforma-tion or broken stones will have happened, which is beyond thehealing capability of asphalt concrete. In addition to its higherhealing rates, porous asphalt concrete containing steel wool hasbetter fatigue resistance than the plain material: it can resist high-er loads with less damage due to the reinforcement of steel wool.Finally, it is expected that the durability of porous asphalt concreteroads will be improved with the induction heating, because of theimprovement in the self-healing capacity and fatigue resistance.The direct effect of this will be less maintenance-activity on theroad and less hinder to traffic. The increase of the lifetime of thepavement will also lead to a decrease in CO2 emission and less en-ergy consumption for production and paving.

Acknowledgements

Authors want to acknowledge the scholarship from the ChinaScholarship Council. In addition, the technical support and goodadvices of Prof. Klaas van Breugel, Prof. André Molenaar and MarcoPoot are also appreciated.

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